1. Field of the Invention
This invention relates to replaceable nozzles for rock bits utilizing drilling fluid to remove detritus from an earthen formation borehole.
More particularly, this invention relates to weld-in sleeves utilized to secure replaceable nozzles in rock bit bodies. The sleeve provides a means to both minimize fluid erosion and assure a more uniform flow of drilling fluid contained within a plenum formed by the rock bit body to the nozzles.
2. Background
Replacement nozzles must have a means of being retained into rock bits. The more typical retention methods for securing nozzles are mechanical and are machined either directly into the bit body or into a sleeve that is in turn welded into bores formed in the rock bit body.
Weld-in nozzle sleeves have been used in rotary cone rock bits for several years for ease of manufacturing. An internal plenum interfaces with secured nozzles via a relatively narrow passage bore formed adjacent to the plenum, of which a portion of the passage way is included in the welded-in sleeve, if a sleeve is utilized.
Internal erosion, in and around nozzle bodies is a major problem. A loss of hydraulic pressure downhole results in a trip out of the borehole and often times the bit is replaced due to the extent of damage to the bit as a result of fluid erosion.
Internal erosion in a rock bit can typically be related to four parameters, mud weight, mud abrasiveness, flow velocity and geometrical discontinuities i.e. gaps, bend, comers and the like. The current nozzle retention configurations are limited in flow capacity by creating a high fluid velocity over a sharp comer formed in the bit adjacent the passage bore entrance. High flow rates cause the fluid flow to separate at the comer creating recirculation zones with sufficient energy to erode the surrounding metal surface that, as heretofore stated, has caused bit washout.
Another potential problem with the state of the art weld-in sleeve is gaps formed between the sleeve and the leg or bit body interface. Gaps may occur at this interface if correct manufacturing procedures are not followed. High fluid flow over gaps where the depth of the gap is much greater than the width will tend to cause recirculation zones within the gap with sufficient energy to erode the surrounding metal potentially leading to bit washout.
The present invention overcomes the above difficulties of the state of the art nozzle retention configurations by designing and securing the sleeve retention configurations in the rock bit body in a way to minimize the possibility of fluid erosion problems.